Multiplexing techniques in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Time Division Multiplexing (TDM)

Which statement best describes how Time Division Multiplexing (TDM) works?

A It assigns different time slots to multiple signals over the same channel sequentially.

B It divides the total bandwidth into frequency bands assigned to each user simultaneously.

C It combines signals by varying the amplitude of a carrier wave for each user.

D It sends multiple signals by encoding them into different polarizations of a wave.

💡 Hint

Think about how signals share the same channel but take turns in using it.

Time Division Multiplexing (TDM) works by dividing the channel into time slots. Each user transmits in their assigned time slot, one after another, sharing the same frequency but at different times.

📋 Factual

intermediate

Frequency Division Multiplexing (FDM) Characteristics

Which of the following is a true characteristic of Frequency Division Multiplexing (FDM)?

A It divides the channel bandwidth into non-overlapping frequency bands for each user.

B It requires synchronization of time slots between users.

C It uses digital encoding to separate signals in the time domain.

D It combines signals by changing the phase of a carrier wave.

💡 Hint

Consider how different users can transmit simultaneously without interfering by using different parts of the spectrum.

Frequency Division Multiplexing (FDM) splits the total bandwidth into separate frequency bands. Each user transmits simultaneously on their own frequency band without overlapping.

🔍 Analysis

advanced

Comparing TDM and FDM Efficiency

Given a communication channel shared by multiple users, which multiplexing technique is generally more efficient when users have bursty data transmissions and why?

A TDM, because it allocates fixed time slots regardless of user activity, ensuring fairness.

B FDM, because it allows users to transmit simultaneously without waiting for time slots.

C TDM, because it can dynamically assign time slots only when users have data to send.

D FDM, because it uses digital encoding to compress data and save bandwidth.

💡 Hint

Think about how time slots can be assigned flexibly versus fixed frequency bands.

Dynamic TDM can assign time slots only when users have data, making it efficient for bursty traffic. Fixed FDM allocates frequency bands continuously, which can waste bandwidth if users are inactive.

🚀 Application

advanced

Identifying Multiplexing Technique from Scenario

A cable TV provider sends multiple TV channels over a single coaxial cable. Each channel occupies a specific frequency band and all channels are transmitted simultaneously. Which multiplexing technique is used here?

A Code Division Multiplexing (CDM)

B Frequency Division Multiplexing (FDM)

C Time Division Multiplexing (TDM)

D Wavelength Division Multiplexing (WDM)

💡 Hint

Think about how different TV channels can be sent at the same time without interfering.

Cable TV uses Frequency Division Multiplexing (FDM) by assigning each channel a unique frequency band, allowing simultaneous transmission over the same cable.

❓ Reasoning

expert

Multiplexing Technique Selection for Optical Networks

In an optical fiber network, multiple data streams are sent simultaneously by using different wavelengths (colors) of light. Which multiplexing technique is this, and why is it preferred over TDM or FDM in this context?

A Code Division Multiplexing (CDM), because it encodes light signals with unique codes.

B Time Division Multiplexing (TDM), because it allows precise timing control of light pulses in fiber.

C Frequency Division Multiplexing (FDM), because it divides the optical spectrum into frequency bands like radio waves.

D Wavelength Division Multiplexing (WDM), because optical fibers can carry multiple wavelengths simultaneously with minimal interference.

💡 Hint

Consider how light properties are used to carry multiple signals in fiber optics.

Wavelength Division Multiplexing (WDM) uses different light wavelengths to send multiple signals simultaneously through the same fiber. It is preferred because optical fibers support many wavelengths with low interference, unlike TDM or FDM which are less practical for light signals.

Practice

1. What is the main purpose of multiplexing in communication systems?

easy

A. To allow multiple signals to share a single communication channel

B. To increase the power of a single signal

C. To encrypt data for secure transmission

D. To convert analog signals to digital signals

Solution

1. Step 1: Understand the concept of multiplexing

   Multiplexing is a technique used to combine multiple signals so they can share one communication channel efficiently.

2. Step 2: Identify the main purpose

   The main goal is to use the channel efficiently by allowing many signals to use it simultaneously, not to increase power, encrypt, or convert signals.

3. Final Answer:

   To allow multiple signals to share a single communication channel -> Option A

4. Quick Check:

   Multiplexing = sharing channel [OK]

Hint: Multiplexing means many signals, one channel [OK]

Common Mistakes:

• Confusing multiplexing with encryption
• Thinking multiplexing increases signal power
• Mixing multiplexing with signal conversion

2. Which of the following is the correct abbreviation for Time Division Multiplexing?

easy

A. TDM

B. FDM

C. WDM

D. CDM

Solution

1. Step 1: Recall common multiplexing abbreviations

   Time Division Multiplexing is abbreviated as TDM, Frequency Division Multiplexing as FDM, Wavelength Division Multiplexing as WDM, and Code Division Multiplexing as CDM.

2. Step 2: Match abbreviation to full form

   Since the question asks for Time Division Multiplexing, the correct abbreviation is TDM.

3. Final Answer:

   TDM -> Option A

4. Quick Check:

   Time Division Multiplexing = TDM [OK]

Hint: T for Time in TDM helps remember [OK]

Common Mistakes:

• Mixing TDM with FDM
• Confusing WDM with CDM
• Assuming CDM stands for Time Division

3. Consider a communication system using Frequency Division Multiplexing (FDM) with 3 channels at frequencies 100 MHz, 110 MHz, and 120 MHz. Which statement is true?

medium

A. Channels transmit one after another in time slots

B. Channels use unique codes to transmit simultaneously

C. All channels transmit at the same time but on different frequencies

D. Channels combine wavelengths to send data

Solution

1. Step 1: Understand Frequency Division Multiplexing (FDM)

   FDM assigns different frequency bands to each channel so they can transmit simultaneously without interference.

2. Step 2: Analyze the given frequencies and options

   The channels at 100 MHz, 110 MHz, and 120 MHz transmit at the same time but on different frequencies, unlike time division or code division multiplexing.

3. Final Answer:

   All channels transmit at the same time but on different frequencies -> Option C

4. Quick Check:

   FDM = simultaneous different frequencies [OK]

Hint: F in FDM means frequency, so different frequencies [OK]

Common Mistakes:

• Thinking FDM uses time slots
• Confusing FDM with CDM code usage
• Assuming wavelength combination applies here

4. A student wrote that in Time Division Multiplexing (TDM), all channels transmit simultaneously on different frequencies. What is the error in this statement?

medium

A. TDM combines wavelengths for transmission

B. TDM uses different codes, not frequencies

C. TDM is only used for analog signals

D. TDM transmits signals one after another in time slots, not simultaneously

Solution

1. Step 1: Review how Time Division Multiplexing works

   TDM divides time into slots and assigns each channel a slot to transmit sequentially, not simultaneously.

2. Step 2: Identify the mistake in the student's statement

   The student incorrectly said channels transmit simultaneously on different frequencies, which describes FDM, not TDM.

3. Final Answer:

   TDM transmits signals one after another in time slots, not simultaneously -> Option D

4. Quick Check:

   TDM = sequential time slots, not simultaneous [OK]

Hint: TDM means time slots, not simultaneous frequencies [OK]

Common Mistakes:

• Confusing TDM with FDM
• Assuming TDM uses codes or wavelengths
• Thinking TDM only works for analog signals

5. In a fiber optic system using Wavelength Division Multiplexing (WDM), four data streams are combined using wavelengths 850 nm, 1310 nm, 1550 nm, and 1625 nm. If one wavelength channel fails, what is the best approach to maintain communication without losing all data?

hard

A. Switch all data streams to a single wavelength immediately

B. Use redundancy by adding backup wavelengths for critical data streams

C. Convert WDM to TDM to avoid wavelength failure

D. Increase the power of the remaining wavelengths to cover the lost one

Solution

1. Step 1: Understand Wavelength Division Multiplexing (WDM) and failure impact

   WDM uses different light wavelengths to carry separate data streams. If one wavelength fails, that data stream is lost unless there is backup.

2. Step 2: Evaluate options to maintain communication

   Adding backup wavelengths (redundancy) for critical streams ensures communication continues even if one channel fails. Switching all streams to one wavelength or increasing power won't solve the failure. Converting to TDM is not practical on the fly.

3. Final Answer:

   Use redundancy by adding backup wavelengths for critical data streams -> Option B

4. Quick Check:

   WDM failure needs backup wavelengths [OK]

Hint: Backup wavelengths keep WDM data safe [OK]

Common Mistakes:

• Trying to merge all streams on one wavelength
• Thinking power increase fixes wavelength failure
• Assuming switching multiplexing types is easy